Dissertations / Theses on the topic 'Analogue gravity'
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1
Doyle, Emma EsmeÌ. "Analogue and numerical modelling of gravity currents and pyroclastic flows." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443693.
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Butera, Salvatore. "Synthetic gauge potentials and analogue gravity in Bose-Einstein condensates." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3260.
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In this thesis multi-component, spinorial cold atomic gases are studied. We investigate first the new perspectives introduced by nonlinear, that is density dependent, synthetic gauge fields in atomic Bose-Einstein condensate. Such fields stem from a collisionally induced detuning in combination with synthetic magnetism arising from the light-atom coupling. The effective mean field dynamics of the condensate shows the appearance of an exotic nonlinearity which is proportional to the current in the system. It introduces a chirality, whose effects on the stability and dynamical properties of the rotating state of a condensate is investigated. We show that by properly shaping the profile and the magnitude of the light-matter interaction parameters, it may happen that the rotating state is energetically favorable compared to the corresponding non-rotating one. Furthermore, we analyze the effects of the nonlinear field on the dynamics of a vortex in a condensate. We obtain the equation of motion for the vortex core, showing the appearance of an extra force which is explicitly depending on the number of particles that are in the system. Furthermore, we consider the implications of the same type of density-dependent fields in the context of analogue gravity. We show that they provide an extra degreeof- freedom that can be exploited in order to design effective non-trivial spacetimes experienced by phonons. In the framework of analogue models of gravity, we finally discuss the perspectives of two-dimensional systems, and address the problem of the black hole lasing effect in the spin modes of the system. By developing a Gross-Pitaevskii theory for the problem, we prove the onset of the lasing instability, and the phenomenon of mode conversion at the horizons. To this aim we consider both homogeneous and harmonically trapped condensates.
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Giacomelli, Luca. "Superradiant phenomena - Lessons from and for Bose-Einstein condensates." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/294551.
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The work of this thesis is guided by the Analogue Gravity research programme, in which condensed matter systems are used as analogues of the physics of curved spacetimes to obtain new perspectives on open problems of gravitational physics. Here we use this idea to investigate the phenomenon of superradiance, most famously occurring in rotating black hole spacetimes, using as an analogue system atomic Bose-Einstein condensates (BECs). Superradiance is a radiation enhancement phenomenon in which waves of different kind are scattered with an increased amplitude by extracting energy from the object they are scattering on. In this thesis on the one hand we use the gravitational analogy to understand better superradiance starting from easier analogue setups, and on the other hand we use concepts coming from superradiance to learn something about the physics of BECs. We first present a (possibly realizable) toy model, built using the tools of synthetic gauge fields for neutral atoms, to provide a new and conceptually simple illustration of superradiant scattering. This toy model allows to disentangle the different elements at play and highlight the basic mechanisms of superradiance and has also the interesting feature of being exactly mappable to a scattering problem of a charged scalar field on an electrostatic potential. We also show how at the quantum level, superradiance implies the spontaneous emission of pairs of excitations. The low temperatures of atomic condensates can make these quantum features visible and we propose a way of detecting them via correlation measurements. Another realization of this toy model can also be built using periodic trapping potentials for the atoms. By changing the boundary conditions of the acoustic excitations of the condensate we show how superradiance can give rise to dynamical instabilities. Our toy model gives a simple illustration of superradiant instabilities occurring in rotating gravitational spacetimes, in particular ergoregion instabilities and black hole bombs. It also provides a realization of the analogous instabilities involving a charged scalar field, called the Schiff-Snyder-Weinberg effect. Our approach naturally shows how amplified scattering can also occur in the presence of dynamical instabilities, a point often object of confusion in the literature. Moreover, we add an acoustic horizon to our toy model and show that, differently from what happens in general relativity, horizons do not always prevent the presence of ergoregion instabilities. We then apply these concepts to the study of the stability of quantized vortices in two-dimensional BECs. With a careful account of boundary conditions, we show that the dynamical instability of multiply quantized vortices in trapped condensates persists in untrapped, spatially homogeneous geometries and has an ergoregion nature with some modification due to the peculiar dispersion of Bogoliubov sound. Our results open new perspectives to the physics of vortices in trapped condensates, where multiply quantized vortices can be stabilized by interference effects and singly charged vortices can become unstable in suitably designed trap potentials. We show how superradiant scattering can be observed also in the short-time dynamics of dynamically unstable systems, providing an alternative point of view on dynamical (in)stability phenomena in spatially finite systems. Finally we consider the equivalent of a shear layer between parallel flows in hydrodynamics, but in a BEC. In the present case the shear layer is constituted by and array of quantized vortices that are shown to develop an instability analogous to the Kelvin-Helmholtz instability. When the relative velocity between the two parallel flow is sufficiently large however, this instability is quenched and substituted by a slower instability that has the features of the superradiant instabilities we studied. Differently from superradiant instabilities, this one also remains with open boundary conditions on the two sides of the shear layer, and manifests itself as a continuous emission of phonons in both directions; we call this new regime radiative instability.
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Giacomelli, Luca. "Superradiant phenomena - Lessons from and for Bose-Einstein condensates." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/294551.
Full textAbstract:
The work of this thesis is guided by the Analogue Gravity research programme, in which condensed matter systems are used as analogues of the physics of curved spacetimes to obtain new perspectives on open problems of gravitational physics. Here we use this idea to investigate the phenomenon of superradiance, most famously occurring in rotating black hole spacetimes, using as an analogue system atomic Bose-Einstein condensates (BECs). Superradiance is a radiation enhancement phenomenon in which waves of different kind are scattered with an increased amplitude by extracting energy from the object they are scattering on. In this thesis on the one hand we use the gravitational analogy to understand better superradiance starting from easier analogue setups, and on the other hand we use concepts coming from superradiance to learn something about the physics of BECs. We first present a (possibly realizable) toy model, built using the tools of synthetic gauge fields for neutral atoms, to provide a new and conceptually simple illustration of superradiant scattering. This toy model allows to disentangle the different elements at play and highlight the basic mechanisms of superradiance and has also the interesting feature of being exactly mappable to a scattering problem of a charged scalar field on an electrostatic potential. We also show how at the quantum level, superradiance implies the spontaneous emission of pairs of excitations. The low temperatures of atomic condensates can make these quantum features visible and we propose a way of detecting them via correlation measurements. Another realization of this toy model can also be built using periodic trapping potentials for the atoms. By changing the boundary conditions of the acoustic excitations of the condensate we show how superradiance can give rise to dynamical instabilities. Our toy model gives a simple illustration of superradiant instabilities occurring in rotating gravitational spacetimes, in particular ergoregion instabilities and black hole bombs. It also provides a realization of the analogous instabilities involving a charged scalar field, called the Schiff-Snyder-Weinberg effect. Our approach naturally shows how amplified scattering can also occur in the presence of dynamical instabilities, a point often object of confusion in the literature. Moreover, we add an acoustic horizon to our toy model and show that, differently from what happens in general relativity, horizons do not always prevent the presence of ergoregion instabilities. We then apply these concepts to the study of the stability of quantized vortices in two-dimensional BECs. With a careful account of boundary conditions, we show that the dynamical instability of multiply quantized vortices in trapped condensates persists in untrapped, spatially homogeneous geometries and has an ergoregion nature with some modification due to the peculiar dispersion of Bogoliubov sound. Our results open new perspectives to the physics of vortices in trapped condensates, where multiply quantized vortices can be stabilized by interference effects and singly charged vortices can become unstable in suitably designed trap potentials. We show how superradiant scattering can be observed also in the short-time dynamics of dynamically unstable systems, providing an alternative point of view on dynamical (in)stability phenomena in spatially finite systems. Finally we consider the equivalent of a shear layer between parallel flows in hydrodynamics, but in a BEC. In the present case the shear layer is constituted by and array of quantized vortices that are shown to develop an instability analogous to the Kelvin-Helmholtz instability. When the relative velocity between the two parallel flow is sufficiently large however, this instability is quenched and substituted by a slower instability that has the features of the superradiant instabilities we studied. Differently from superradiant instabilities, this one also remains with open boundary conditions on the two sides of the shear layer, and manifests itself as a continuous emission of phonons in both directions; we call this new regime radiative instability.
5
De, Vito Marco. "Analytic aspects of analogue Hawking radiation in Bose-Einstein condensates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25570/.
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We present a theoretical study of analogue Hawking effect in stepwise models of Bose-Einstein condensates. We focus on subsonic-supersonic configuration, where two stationary homogeneous condensates are connected by a step-like discontinuity in the local speed of sound. We provide a detailed analysis of the scattering processes of fluctuation modes at the sonic horizon based on microscopic Bogoliubov theory of dilute BECs. Spontaneous phonon emission is predicted to occur at the
horizon as a conversion of vacuum fluctuations into on-shell real particles. The condensed-matter analogue of Hawking radiation arises as a thermal Bose spectrum to low frequency order in the subsonic region. Stepwise BEC configurations with an extended sonic region are also taken into account in order to address more
general and realistic velocity flow profiles.
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Coutant, Antonin. "On the phenomenology of quantum gravity : stability properties of Hawking radiation in the presence of ultraviolet violation of local Lorentz invariance." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112213/document.
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Dans cette thèse, nous étudions plusieurs aspects de la radiation de Hawking en présence de violations de l'invariance locale de Lorentz. Ces violations sont introduites par une modification de la relation de dispersion, devenant non-linéaire aux courtes longueurs d’onde. Les principales motivations de ces travaux ont une double origine. Il y a d’une part le développement en matière condensée de trous noirs analogues, ou l’écoulement d’un fluide est perçu comme une métrique d’espace-temps pour les ondes de perturbations et ou la radiation de Hawking pourrait être détectée expérimentalement. D’autre part, il se pourrait que des effets de gravité quantique puissent être modélisés par une modification de la relation de dispersion. En premier lieu, nous avons obtenu des caractérisations précises des conditions nécessaires au maintien de l’effet Hawking en présence de violation de l’invariance de Lorentz. De plus, nous avons étudié l’apparition d’une onde macroscopique de fréquence nulle, dans des écoulements de type trous blancs et également pour des champs massifs. Une autre partie de ce travail a consisté à analyser une instabilité engendrée par les effets dispersifs, ou la radiation de Hawking est auto-amplifiée, générant ainsi un flux sortant exponentiellement croissant dans le tempsIn this thesis, we study several features of Hawking radiation in the presence of ultraviolet Lorentz violations. These violations are implemented by a modified dispersion relation that becomes nonlinear at short wavelengths. The motivations of this work arise on the one hand from the developing field of analog gravity, where we aim at measuring the Hawking effect in fluid flows that mimic black hole space-times, and on the other hand from the possibility that quantum gravity effects might be approximately modeled by a modified dispersion relation. We develop several studies on various aspects of the prob- lem. First we obtain precise characterizations about the deviations from the Hawking result of black hole radiation, which are induced by dispersion. Second, we study the emergence, both in white hole flows or for massive fields, of a macroscopic standing wave, spontaneously produced from the Hawking effect, and known as ‘undulation’. Third, we describe in detail an instability named black hole laser, which arises in the presence of two horizons, where Hawking radiation is self-amplified and induces an exponentially growing in time emitted flux
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Wuester, Sebastian, and sebastian wuester@gmx net. "Classical and Quantum Field Theory of Bose-Einstein Condensates." The Australian National University. Faculty of Science, 2007. http://thesis.anu.edu.au./public/adt-ANU20070802.161045.
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We study the application of Bose-Einstein condensates (BECs) to simulations of phenomena across a number of disciplines in physics, using theoretical and computational methods.
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Collapsing condensates as created by E. Donley et al. [Nature 415, 39 (2002)]
exhibit potentially useful parallels to an inflationary universe. To enable the exploitation of this analogy, we check if current quantum field theories describe collapsing condensates quantitatively, by targeting the discrepancy between experimental and theoretical values for the time to collapse. To this end, we couple the lowest order quantum field correlation functions to the condensate wavefunction, and solve the resulting Hartree-Fock-Bogoliubov equations numerically. Complementarily, we perform stochastic truncated Wigner simulations of the collapse. Both methods also allow us to study finite temperature effects.
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We find with neither method that quantum corrections lead to a faster collapse than is predicted by Gross-Pitaevskii theory. We conclude that the discrepancy between the experimental and theoretical values of the collapse time cannot be explained by Gaussian quantum fluctuations or finite temperature effects.
Further studies are thus required before the full analogue cosmology potential of collapsing condensates can be utilised.
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As the next project, we find experimental parameter regimes in which stable three-dimensional Skyrmions can exist in a condensate. We show that their stability in a harmonic trap depends critically on scattering lengths, atom numbers, trap rotation and trap anisotropy. In particular, for the Rb87 |F=1,m_f=-1>, |F=2,m_f=1> hyperfine states, stability is sensitive to the scattering lengths at the 2% level. We find stable Skyrmions with slightly more than 2*10^6 atoms, which can be stabilised against drifting out of the trap by laser pinning.
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As a stepping stone towards Skyrmions, we propose a method for the stabilisation of a stack of parallel vortex rings in a Bose-Einstein condensate. The method makes use of a ``hollow'' laser beam containing an optical vortex, which realises an optical tunnel for the condensate. Using realistic experimental parameters, we demonstrate numerically that our method can stabilise up to 9 vortex rings.
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Finally, we focus on analogue gravity, further exploiting the analogy between flowing condensates and general relativistic curved space time. We compare several realistic setups, investigating their suitability for the observation of analogue Hawking radiation. We link our proposal of stable ring flows to analogue gravity, by studying supersonic flows in the optical tunnel. We show that long-living immobile condensate solitons generated in the tunnel exhibit sonic horizons, and discuss whether these could be employed to study extreme cases in analogue gravity.
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Beyond these, our survey indicates that for conventional analogue Hawking radiation,
simple outflow from a condensate reservoir, in effectively one dimension, has the best properties. We show with three dimensional simulations that stable sonic horizons exist under realistic conditions. However, we highlight that three-body losses impose limitations on the achievable analogue Hawking temperatures. These limitations vary between the atomic species and favour light atoms.
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Our results indicate that Bose-Einstein condensates will soon be useful for interdisciplinary studies by analogy, but also show that the experiments will be challenging.
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Euvé, Léo-Paul. "Interactions ondes-courant-obstacle : application à la physique des trous noirs." Thesis, Poitiers, 2017. http://www.theses.fr/2017POIT2280/document.
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Le projet de recherche consiste à observer en laboratoire la radiation de Hawking, cette prédiction stupéfiante de l'astrophysicien anglais Stephen Hawking faite en 1974 : les trous noirs ne sont pas noirs. Autrement dit, ils n'absorbent pas tout ce qui est à leur portée mais émettent un rayonnement. En plus des complications du fait que ces objets célestes sont à des milliers d'années-lumière, ce rayonnement est tellement faible que cela reviendrait à essayer d'entendre un murmure dans un concert de rock. Mais William Unruh, en 1981, a proposé une solution : utiliser des systèmes hydrodynamiques qui présentent les mêmes équations mathématiques qu'en astrophysique. Plus précisément, dans notre cas, nous utilisons la correspondance entre la propagation des ondes lumineuses au voisinage d'un trou noir et celles des ondes de surface dans un contre-courant rendu inhomogène par la présence d'un obstacle immergé. Pour cela, une compréhension approfondie de la mécanique des ondes de surface est nécessaire (bathymétrie variable, vorticité, non-linéarités…). Du côté technique, une méthode de mesure de surface libre a été développée et optimiséeThe aim of the PhD is the observation the Hawking radiation in the laboratory, this astounding prediction of the English astrophysicist Stephen Hawking made in 1974: black holes are not black. In other words, they do not absorb anything within reach but emit a radiation. In addition to the complications of the fact that these celestial objects are thousands of light years away, this radiation is so weak that it would be like trying to hear a whisper in a rock concert. But William Unruh, in 1981, proposed a solution: to use hydrodynamic systems which have the same mathematical equations as in astrophysics. More precisely, in our case, we use the correspondence between the propagation of light in the vicinity of a black hole and surface waves propagation on a inhomogeneous countercurrent (due to the presence of a submerged obstacle). For this, a thorough understanding of the surface waves physics is necessary (variable bathymetry, vorticity, non-linearities ...). On the technical side, a free surface measurement method has been developed and optimized
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Aruquipa, David Quispe 1989. "An analogue model of gravity based on a radial fluid flow : the case of AdS and its deformations = Um modelo análogo à gravitação baseado em um fluxo radial: o caso do espaço-tempo AdS e suas deformações." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/325326.
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Orientadores: Ricardo Antonio Mosna, Márcio José MenonDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-09-02T03:12:41Z (GMT). No. of bitstreams: 1 QuispeAruquipa_David_M.pdf: 2372918 bytes, checksum: bb030f9f8aecc210d608f2f9005a7a49 (MD5) Previous issue date: 2017
Resumo: Os modelos análogos são uma ferramenta muito útil quando se quer entender ou testar fenômenos em um sistema físico em termos e conceitos de outro, esses sistemas podem ser mais familiares ou mais facilmente reproduzíveis por experimentos. Este trabalho explora esta questão no contexto de modelos análogos à gravitação baseados na mecânica dos fluidos. Particularmente, estamos interessados em fornecer um modelo análogo para um fluxo radial com uma fonte/sorvedouro na origem. Começamos por considerar o caso em que a velocidade do fluxo (radial) é constante. O modelo análogo resultante é então o espaço-tempo Anti-de Sitter (ou AdS) que é conhecido por ser não-globalmente hiperbólico. Como resultado, a dinâmica dos campos neste contexto não está bem definida até que sejam estabelecidas condições adicionais na fronteira no infinito espacial do espaço-tempo AdS. A contrapartida destas condições de fronteira extra na mecânica dos fluidos proporciona uma descrição efetiva da fonte/sorvedouro que está na origem. Depois disso, nós consideramos regularizações para o modelo análogo perto da fonte/sorvedouro na origem. Logo, impomos condições sobre eles, a fim de que a dinâmica seja bem definida de modo que não são mais necessárias as condições na fronteira. Calculamos como as quantidades físicas, como a diferença de fase entre as ondas que entram e saem, são afetadas pelas regularizações. Estes resultados são então comparados com o caso AdS para compreender as principais implicações do processo de regularização, que tem o efeito de deformar a região perto do infinito espacial do AdS. Mostramos também que, sob certas condições, a diferença de fase obtida para esses espaços deformados do AdS coincide com a obtida no caso do espaço-tempo AdS
Abstract: Analogue models are a useful tool when one wants to understand or probe phenomena in one physical system in terms of concepts from another, which may be more familiar or more easily accessed by experiments. This work explores this framework in the context of analogue models of gravity based on fluid dynamics. Particularly, we are interested in providing an analogue model for a radial fluid flow with a point source/sink at the origin. We start by considering the case where the (radial) flow velocity is constant. The resulting analogue model is then the Anti-de Sitter spacetime (AdS) which is known to be non-globally hyperbolic. As a result, the dynamics of fields in this background is not well defined until extra boundary conditions at its spatial boundary are prescribed. The fluid dynamics counterpart of these extra boundary conditions provide an effective description of the point source/sink at the origin. After that, we consider regularizations of this model near the source/sink at the origin. We then impose conditions on them in order that the dynamics is well defined so that no extra boundary conditions are required. We calculate how physical quantities, like the phase difference between ingoing and outgoing scattered waves are affected by the regularizations. These results are then compared with the AdS case to understand the main implications of the regularization, which has the effect of deforming the AdS space near its spatial infinity. We also show that, under certain conditions, the phase difference obtained for these deformed AdS spaces agrees with that obtained in the AdS case
Mestrado
Física
Mestre em Física
1490213/2015
CAPES
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Isoard, Mathieu. "Theoretical study of quantum correlations and nonlinear fluctuations in quantum gases." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP004.
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Cette thèse est dédiée à l’étude des phénomènes non-linéaires dans deux fluides quantiques qui partagent de nombreuses similitudes : les condensats de Bose-Einstein et les “fluides de lumière”. Dans une première partie, nous étudions les analogues soniques des trous noirs. Il est possible de créer une configuration stationnaire d’un condensat de Bose-Einstein en écoulement d’une région subsonique vers une région supersonique. Ce fluide transsonique joue alors le rôle d’un trou noir puisque les ondes sonores ne peuvent s’échapper de la région supersonique. En outre, en quantifiant le champ sonore, il est possible de montrer qu’un rayonnement de Hawking analogue émerge des fluctuations quantiques du vide. Dans cette thèse, nous montrons que la prise en compte des “modes zéros” – omis jusqu’alors dans le contexte de la gravité analogue – est essentielle pour obtenir une description précise du processus de Hawking, menant alors à un excellent accord avec les résultats expérimentaux. Enfin, nous étudions l’intrication entre les différentes excitations quantiques et montrons que notre système crée de l’intrication tripartite. Dans un second temps, nous étudions la propagation des fluides non-linéaires grâce à une approche hydrodynamique et à des méthodes mathématiques développées par Riemann et Whitham. Nous étudions la structure oscillante et la dynamique des ondes de chocs dispersives qui se forment à la suite d’un déferlement. Notre approche permet de trouver des expressions analytiques simples qui décrivent les propriétés asymptotiques du choc. Cela donne accès à des paramètres d’intérêt expérimental, comme le temps de déferlement, la vitesse de l’onde de choc ou encore le contraste de ses frangesThis thesis is dedicated to the study of nonlinear-driven phenomena in two quantum gases which bear important similarities: Bose-Einstein condensates of ultracold atomic vapors and “fluids of light”. In a first part, we study sonic analogues of black holes. In a Bose-Einstein condensate, it is possible to implement a stationary configuration with a current flowing from a subsonic region to a supersonic one. This mimics a black hole, since sonic excitations cannot escape the supersonic region. Besides, quantizing the phonon field leads to a sonic analogue of Hawking radiation. In this thesis, we show that a correct account of “zero modes” – overlooked so far in the context of analogue gravity – is essential for an accurate description of the Hawking process, and results in a excellent comparison with recent experimental data. In addition, we characterize the entanglement shared among quantum excitations and show that they exhibit tripartite entanglement. In a second part, we investigate the short and long time propagation of nonlinear fluids within a hydrodynamic framework and by means of mathematical methods developed by Riemann and Whitham. In particular, we study the oscillating structure and the dynamics of dispersive shock waves which arise after a wave breaking event. We obtain a weak shock theory, from which we can extract a quantitative description of experimentally relevant parameters, such as the wave breaking time, the velocity of the solitonic edge of the shock or the contrast of its fringes
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Robertson, Scott James. "Hawking radiation in dispersive media." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1900.
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Hawking radiation, despite its presence in theoretical physics for over thirty years, remains elusive and undetected. It also suffers, in its original context of gravitational black holes, from conceptual difficulties. Of particular note is the trans-Planckian problem, which is concerned with the apparent origin of the radiation in absurdly high frequencies. In order to gain better theoretical understanding and, it is hoped, experimental verification of Hawking radiation, much study is being devoted to systems which model the spacetime geometry of black holes, and which, by analogy, are also thought to emit Hawking radiation. These analogue systems typically exhibit dispersion, which regularizes the wave behaviour at the horizon but does not lend itself well to analytic treatment, thus rendering Hawking’s prediction less secure. A general analytic method for dealing with Hawking radiation in dispersive systems has proved difficult to find. This thesis presents new numerical and analytic results for Hawking emission spectra in dispersive systems. It examines two black-hole analogue systems: it begins by introducing the well-known acoustic model, presenting some original results in that context; then, through analogy with the acoustic model, goes on to develop the lesser-known fibre-optical model. The following original results are presented in the context of both of these models: • an analytic expression for the low-frequency temperature is found for a hyperbolic tangent background profile, valid in the entire parameter space; it is well-known that the spectrum is approximately thermal at low frequencies, but a universally valid expression for the corresponding temperature is an original development; • an analytic expression for the spectrum, valid over almost the entire frequency range, when the velocity profile parameters lie in the regime where the low-frequency temperature is given by the Hawking prediction; previous work has focused on the low-frequency thermal spectrum and the characterization of the deviations from thermality, rather than a single analytic expression; and • a new unexplored regime where no group-velocity horizon exists is examined; the Hawking spectra are found to be non-zero here, but also highly non-thermal, and are found, in the limit of small deviations, to vary with the square of the maximum deviation; the analytic expression for the case with a horizon is found to carry over to this new regime, with appropriate modifications. Furthermore, the thesis examines the results of a classical frequency-shifting experiment in the context of fibre-optical horizons. The theory of this process is presented for both a constant-velocity and a constantly-decelerating pulse, the latter case taking account of the Raman effect. The resulting spectra are at least qualititively explained, but there is a discrepancy between theory and experiment that has not yet been accounted for.
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Yuan, Xiaoping. "Extensional collapses in the overpressured frictional upper crust based on limit analysis." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEE009/document.
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Dans ce manuscrit nous développons l'approche cinématique 2D du calcul à la rupture pour examinerles effondrements en extension (ou failles normales) de la croûte supérieure cassante qui résultent desurpressions de fluides. Les sujets d'intérêt liés à la déformation en extension sont (1) les roles de lapression des fluides, des processus de surface, et des propriétés des matériaux et des failles sur lastabilité des structures d'extension; (2) la formation de failles normales à faible pendage et de failleslistriques; (3) la distribution de la déformation au dessus d'un glissement à faible pendage; et (4)l'influence de l'adoucissement mécanique des failles et des processus de sédimentation sur cettedistribution.Cette approche mécanique est vérifiée par la théorie du prisme critique de Coulomb, et la généralise pour étudier la topographie complexe de la péninsule de Mejillones dans le Nord du Chili. Cetteapproche est aussi appliquée à l'instabilité gravitaire dans le delta du Niger en reliant les structurescompressives en bas de pente aux structure extensives en amont par un détachement profond. Nousprédisons des surpressions de fluides beaucoup plus élevée que celles obtenues par application duprisme de Coulomb. Enfin, cette méthodologie est appliquée à l'étude de la forme de failles normalesreliant un détachement profond à la surface. Dans le cas du delta du Niger, nous montrons que lesfailles à faible pendage et les failles listriques impliquent que la profondeur de rétention des fluides estfaible. La version séquentielle de l'analyse limite ouvre de nouvelles voies pour suivre l'évolutionstructurale dans le temps du jeu sur les failles normales. Les simulations montrent en particulier qu'unefaille normale tourne vers des pendage plus faibles au fur et à mesure de la dénudation du mur, formantune région qui passe du mur au toit de la faille active en rotation. La prédiction de cette région estillustrée par des expériences analogiques et des exemples de terrainThis manuscript develops a 2D kinematic approach of Limit Analysis to examine the extensionalfailures in the brittle, upper crust resulting from fluid overpressures and normal faulting. There aremany interesting topics related to the extensional deformation such as (1) the roles of fluid pressure,topographic process, material and fault properties on the stability of extensional structures; (2) theformation of low-angle and listric normal fault; (3) the deformation pattern due to slip on a low-anglefault; and (4) the influence of fault softening and sedimentation processes on this deformation pattern.This mechanical approach applied to wedge prototypes is validated by the critical Coulomb wedge(CCW) theory, and it generalizes the CCW theory to investigate the complex topography on theMejillones peninsula, Northern Chile. Additionally, this approach is also applied to investigate gravityinstability of Niger Delta by linking down-slope compressional to up-slope extensional failures througha deep detachment. We predict much higher fluid overpressures than that of the CCW theory. Finally,this Limit Analysis methodology is applied to investigate the shape of normal fault linking a lowdetachment to the surface. The application to Niger Delta implies that the formation of very low-angleand strongly listric faults results from a shallow fluid-retention depth. The sequential version of LimitAnalysis opens new ways to envision the structural evolution through time resulting from normalfaulting. The simulations show that the normal fault rotates during extension, forming a region of Footto-Hanging Wall (FHW) where the material in the footwall is sheared upon entering the hanging wall.The creation of the FHW region is illustrated by sandbox experiments and field examples
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Busch, Xavier. "Effets dispersifs et dissipatifs en théorie quantique des champs en espace-temps courbe pour modéliser des systèmes de matière condensée." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112205/document.
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Les deux principales prédictions de la théorie quantique des champs en espace-temps courbe, à savoir la radiation de Hawking et la production de paires de particules ayant lieu dans un espace-temps non stationnaire, n'ont jamais été testé expérimentalement et impliquent toutes deux des processus à ultra haute énergie. En conséquence, de telles prédictions doivent être considérées prudemment. En utilisant l'analogie avec des systèmes de matière condensée mise en avant par Unruh, leur analogue pourrait être testé en laboratoire. Par ailleurs, dispersion et dissipation sont toujours présentes dans de tels systèmes, ce qui régularise la théorie à courte distances. Lors d'expériences destinées à tester les prédictions citées ci-dessus, le bruit thermique modifiera le résultat. En effet, il existe une compétition entre l'émission stimulée dudit bruit thermique et l'émission spontanée issue du vide quantique. Afin de mesurer la radiation de Hawking analogue et de l'analogue des productions de paires (souvent appelé effet Casimir dynamique), il est alors nécessaire de calculer les conséquence de la dispersion et de la dissipation, ainsi que d'identifier des observables permettant de certifier que l'amission spontanée a eu lieu. Dans cette thèse, nous analyserons d'abord les effets de la dispersion et de la dissipation à la fois sur la radiation de Hawking et sur la production de paires de particules. Afin d'obtenir des résultats explicites, nous travaillerons avec l'espace-temps de de Sitter. Les symétries de la théorie nous permettront d'obtenir des résultats exacts. Ceux-ci seront alors appliqués aux trous noirs grâce aux ressemblances entre la région proche du trou noir et l'espace de de Sitter. Afin d’introduire de la dissipation, nous considérerons un modèle exactement soluble permettant de modéliser n'importe quel taux de dissipation. Dans un tel modèle, le champ est couplé de manière linéaire à un environnement contenant un ensemble dense de degrés de liberté. Dans un tel contexte, nous étudierons l'intrication des particules produites. Ensuite, nous considérerons des systèmes de matière condensée spécifiques, à savoir les condensats de Bose et les polaritons. Nous analyserons les effets de la dissipation sur l'intrication de l’effet Casimir dynamique. Enfin, nous étudieront de manière générique l'intrication de la radiation de Hawking en présence de dispersion pour des systèmes analoguesThe two main predictions of quantum field theory in curved space-time, namely Hawking radiation and cosmological pair production, have not been directly tested and involve ultra high energy configurations. As a consequence, they should be considered with caution. Using the analogy with condensed matter systems put forward by Unruh, their analogue versions could be tested in the lab. Moreover, the high energy behavior of these systems is known and involved dispersion and dissipation, which regulate the theory at short distances. When considering experiments which aim to test the above predictions, the thermal noise will contaminate the outcome. Indeed, there will be a competition between the stimulated emission from thermal noise and the spontaneous emission out of vacuum. In order to measure the quantum analogue Hawking radiation, or the analogue pair production also called dynamical Casimir effect, one should thus compute the consequences of ultraviolet dispersion and dissipation, and identify observables able to establish that the spontaneous emission took place. In this thesis, we first analyze the effects of dispersion and dissipation on both Hawking radiation and pair particle production. To get explicit results, we work in the context of de Sitter space. Using the extended symmetries of the theory in such a background, exact results are obtained. These are then transposed to the context of black holes using the correspondence between de Sitter space and the black hole near horizon region. To introduce dissipation, we consider an exactly solvable model producing any decay rate. In such a model, the field is linearly coupled to an environment containing a dense set of degrees of freedom. We also study the quantum entanglement of the particles so produced. In a second part, we consider explicit condensed matter systems, namely Bose Einstein condensates and exciton-polariton systems. We analyze the effects of dissipation on entanglement produced by the dynamical Casimir effect. As a final step, we study the entanglement of Hawking radiation in the presence of dispersion for a generic analogue system
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Peschler, Anne P. "Archean tectonics: Analog and gravity models." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/29186.
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This work investigates Archean continental geodynamics. Three cratonic areas were studied: the Pilbara Craton, Australia (3.5--3.2 Ga), the Yilgarn Craton, Australia (2.7 Ga) and the Abitibi Subprovince, Canada (2.7 Ga). Each region is modeled using several 2-D gravity profiles. In the 3.5 Ga Pilbara craton, some modeled batholiths have well defined roots that extend to depths greater than 10 km whereas others have roots extending to less than 6 km depth. The model results from the 2.7 Ga Yilgarn craton and the Abitibi Subprovince show no major differences between the two terranes. The rarity of deep roots and a thickness of 5 to 6 km are characteristics of the ca. 2.7 Ga batholiths. The surrounding greenstones form keels of up to 10 km depth, in the three modeled regions. Compassion of the results from the older and younger cratons suggests: (1) the presence (Middle Archean) or quasi-absence (Late Archean) of deep batholith roots may indicate changes in continental geodynamics from 3.5 Ga to 2.8 Ga. (2) greenstones in the Middle and Late Archean terranes form deep keels, which are consistent with the gravity driven, diapiric model in the case of the older greenstones, and may be explained by crustal folding in the younger cases. A more detailed gravity study was done on the Abitibi Subprovince using modeled gravity profiles and a wavelet based inversion method, leading to a new proposed model to explain the structures of the Abitibi Subprovince. In this model the Abitibi upper-middle crust is folded, the deformations zones interpreted as detachment folds. We used analog experiments to investigate folding of continental crust subjected to different geothermal gradients. In our experiments, folding is the main response to shortening of the analog crust. The middle and lower crust analogs respond to the shortening by buckling. In the upper crust analog, detachment folds, thrust faults and grabens above anticlines are developed. For the lowest thermal gradient, one anticline-syncline pair is formed. For warmer gradients, multiple folds develop that have smaller amplitudes. Based on our models, we interpret that the increase of crustal temperatures may result in a decrease of the amplitude of the crustal folds. Our results suggest that the deformation style preserved within Archean greenstone belts is strongly influenced by the syndeformational thermal regime of the crust.*
*This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.
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Michel, Florent. "Effets non-linéaires et effets quantiques en gravité analogue." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS164/document.
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Cette thèse concerne l'étude des propriétés de champs scalaires classiques et quantiques en présence d'un environnement inhomogène et/ou dépendant du temps. Nous nous concentrerons sur des modèles pouvant être décrits, fondamentalement ou de manière effective, par un espace-temps courbe contenant un horizon des événements. Nous verrons en particulier comment une correspondance mathématique, provenant d'une symétrie de Lorentz effective à basse énergie, permet de relier les comportements des ondes dans un cadre non relativiste à la physique des trous noirs, quelles en sont les limites et dans quelle mesure les résultats ainsi obtenus sont og analogues fg à leurs pendants gravitationnels. Après un premier chapitre d'introduction rappelant quelques bases de relativité générale puis une dérivation de la radiation de Hawking et de la correspondance avec des systèmes non relativistes, je présenterai le détail de quatre travaux effectués durant ma thèse. Les autres articles écrits dans ce cadre sont résumés dans le dernier chapitre, précédant une conclusion générale. Mes collaborateurs et moi nous sommes concentrés sur trois aspects du comportement des champs près de l'analogue d'un horizon des événements dans des modèles avec une symétrie de Lorentz effective à basse énergie. Le premier concerne les effets non linéaires, cruciaux pour comprendre l'évolution de la radiation de Hawking ainsi que pour les réalisations expérimentales mais auparavant peu étudiés. Nous montrerons comment ceux-ci déterminent les possibles comportements aux temps longs pour des systèmes stables ou instables. Le second aspect a trait aux effets linéaires et quantiques, en particulier la radiation de Hawking elle-même, son devenir lorsque l'horizon est continûment effacé, ainsi que les diverses instabilités à même de survenir dans différents modèles. Enfin, nous avons participé à l'élaboration, à l'analyse et à l'étude d’expériences dites de og gravité analogue fg dans des condensats de Bose-Einstein et des systèmes hydrodynamiques ou acoustiques, dont je rapporte les principaux résultatsThe present thesis deals with some properties of classical and quantum scalar fields in an inhomogeneous and/or time-dependent background, focusing on models where the latter can be described as a curved space-time with an event horizon. While naturally formulated in a gravitational context, such models extend to many physical systems with an effective Lorentz invariance at low energy. We shall see how this effective symmetry allows one to relate the behavior of perturbations in these systems to black-hole physics, what are its limitations, and in which sense results thus obtained are “analogous” to their general relativistic counterparts. The first chapter serves as a general introduction. A few notions from Einstein's theory of gravity are introduced and a derivation of Hawking radiation is sketched. The correspondence with low-energy systems is then explained through three important examples. The next four chapters each details one of the works completed during this thesis, updated and slightly reorganized to account for new developments which occurred after their publication. The other articles I contributed to are summarized in the last chapter, before the general conclusion. My collaborators and I focused on three aspects of the behavior of fields close to the (analogue) event horizon in models with an effective low-energy Lorentz symmetry. The first one concerns nonlinear effects, which had been given little attention in view of their crucial importance for understanding the evolution in time of Hawking radiation as well as for experimental realizations. We showed in particular how they determine the late-time behavior in stable and unstable configurations. The second aspect concerns linear and quantum effects. We studied the Hawking radiation itself in several models and what replaces it when continuously erasing the horizon. We also characterized and classified the different types of linear instabilities which can occur. Finally, we contributed to the design and analysis of “analogue gravity” experiments in Bose-Einstein condensates, hydrodynamic flows, and acoustic setups, of which I report the main results
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Flayac, Hugo. "Nouvelles tendances dans les condensats d'exciton-polaritons spineurs : défauts topologiques et structures de basse dimensionnalité." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00822148.
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Au long de ce manuscrit de thèse je présenterai des effets non linéaires émergents dans les condensats d'exciton-polaritons spineurs. Après un chapitre d'introduction amenant les notions de bases nécessaires, je me concentrerai dans une première partie sur les défauts topologiques quantifiés par des nombres demi-entiers et discuterai leur stabilité, accélération et nucléation en présence de champs magnétiques effectifs. Nous verrons que ces objets se comportent comme des charges magnétiques manipulables démontrant une analogie fascinante avec les monopoles de Dirac. De manière remarquable nous verrons également que ces objets peuvent être utilisés comme des signaux stables pour sonder la physique d'analogues acoustiques de trous noirs. Dans une seconde partie j'étudierai des structures de basse dimensions. Plus particulièrement, je décrirai la formation de solitons de bande interdite et les oscillations de Bloch des exciton-polaritons dans des microfils comportant des structures périodiques et d'autre part les oscillations Josephson à température ambiante dans des paires de micropilliers couplés.
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Coutant, Antonin. "phénoménologie de la gravité quantique : Propriété de stabilité de la radiation d'Hawking en présence de violation de l'invariance local de Lorentz." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00747874.
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Dans cette thèse, nous étudions plusieurs aspects de la radiation de Hawking en présence de violations de l'invariance locale de Lorentz. Ces violations sont introduites par une modification de la relation de dispersion, devenant non-linéaire aux courtes longueurs d'onde. Les principales motivations de ces travaux ont une double origine. Il y a d'une part le développement en matière condensée de trous noirs analogues, ou l'écoulement d'un fluide est perçu comme une métrique d'espace-temps pour les ondes de perturbations et ou la radiation de Hawking pourrait être détectée expérimentalement. D'autre part, il se pourrait que des effets de gravité quantique puissent être modélisés par une modification de la relation de dispersion. En premier lieu, nous avons obtenu des caractérisations précises des conditions nécessaires au maintien de l'effet Hawking en présence de violation de l'invariance de Lorentz. De plus, nous avons étudié l'apparition d'une onde macroscopique de fréquence nulle, dans des écoulements de type trous blancs et également pour des champs massifs. Une autre partie de ce travail a consisté à analyser une instabilité engendrée par les effets dispersifs, ou la radiation de Hawking est auto-amplifiée, générant ainsi un flux sortant exponentiellement croissant dans le temps.
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Schueller, Sylvie. "Localisation de la déformation et fracturation associée: Etude expérimentale et numérique sur des analogues de la lithosphère continentale." Rennes 1, 2004. https://tel.archives-ouvertes.fr/tel-00009829.
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L'étude de la localisation de la déformation dans un milieu fragile/ductile s'inscrit dans la compréhension mécanique du développement des réseaux de fractures multi-échelles, caractéristiques de la déformation intra-continentale. La modélisation expérimentale, simulant un contexte de collision à l'échelle lithosphérique, permet de définir les conditions nécessaires à la localisation de la déformation, fonction des forces gravitaires et du couplage fragile/ductile. L'analyse détaillée des champs de déformation conduit à caractériser l'évolution temporelle et spatiale de la localisation, ainsi que ses relations avec les paramètres mécaniques. L'étude met en évidence une organisation spatiale multi-échelle des hétérogénéités de déformation, caractérisée par une dimension fractale ; celle-ci dépend du couplage fragile/ductile dont le rôle mécanique est étudié numériquement. Une bonne adéquation entre localisation de la déformation et croissance des failles est par ailleurs constatée.
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Lind, Karin, and Maria Trång. "Effekten av kinesiotejpning på aktivitetsförmåga och smärta hos gravida med pelvic girdle pain – en pilotstudie." Thesis, Uppsala University, Physiotheraphy, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-126701.
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Syftet var att undersöka om kinesiotejpning kunde påverka aktivitetsförmåga och smärta hos gravida kvinnor med pelvic girdle pain. Studien var en single subjekt experimentell AB-design. Fyra kvinnor inkluderades i pilotstudien för behandling av pelvic girdle pain. Smärtan skattades och mättes med visuell analog skala. Aktivitetsförmågan mättes med Roland & Morris disability questionnaire.
Resultatet visade att gällande aktivitetsförmåga kunde det med 95 % säkerhet ses en förbättring hos tre av kvinnorna. Gällande smärtskattningen kunde endast hos en kvinna på kvällen och hos en annan kvinna på morgonen och kvällen ses en kliniskt signifikant minskad smärta. Resultaten i studien ger underlag för att en mer omfattande randomiserad och kontrollerad klinisk studie bör genomföras.
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Michel, Laure. "Transport en fracture et interaction avec la matrice : une expérience analogique." Phd thesis, Université Rennes 1, 2009. http://tel.archives-ouvertes.fr/tel-00507846.
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Nous caractérisons en laboratoire le transport de solutés dans une fracture unique à paroi inférieure poreuse et l'interaction fracture-matrice durant ce transport. Notre dispositif expérimental en Plexiglas est constitué d'une fracture synthétique (100 cm de long, 5 cm de large, 0,5 cm de haut) présentant une interface inférieure imperméable (Plexiglas) ou perméable (couche de billes de verre). Un flux d'eau est imposé à travers la fracture à des vitesses moyennes contrôlées (~1 mm/s). Un système d'injection de colorant simule au centre de la fracture une source ponctuelle de contaminant, dont la migration est décrite par l'évolution spatio-temporelle de la concentration grâce à un système de mesures optiques. Le dispositif s'est révélé bien adapté à l'étude du couplage densitaire entre écoulement et transport dans une fracture imperméable en régime pré-asymptotique. La mesure à intervalles réguliers du flux massique advectif bidimensionnel associé au panache de soluté permet d'établir des profils de la masse m(x) qui traverse une section de fracture transverse à l'écoulement à la position longitudinale x. Une quantité de soluté piégée à la surface du milieu poreux, même sans réelle diffusion dans le milieu, est « vue » par le dispositif de mesure comme de la masse perdue, et donc échangée. Des pertes de masses significatives par rapport à notre incertitude expérimentales sont mesurées pour une fracture dont la paroi inférieure poreuse présente une rugosité ondulée. Cette configuration géométrique crée des zones de faibles vitesses permettant le piégeage superficiel d'une partie du soluté (jusqu'à 30%). Les effets gravitaires jouent un rôle prépondérant dans ce processus.
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Horta, Bernús Ricard. "Lleis d'escala i complexitat estructural de les infraestructures tecnològiques. Els sistemes biològics com a analogia pel disseny i optimització del transport i distribució de l'energia elèctrica." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/145689.
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Within the paradigm of sustainability, this thesis aims to provide complementary views to the conventional engineering in order to put forward tools that facilitate, on the one hand the search of solutions to improve the design of high-voltage power lines , and on the other hand to optimize their networks. As per the improving of a high-voltage line design, Scaling Laws and Gravity Models are used to provide new variables to estimate calculation of the electricity demand of a certain area. This article proposes modifications to the vector diagram of a transmission line operation, known as a Perrine-Baum Diagram to incorporate the new variables proposed with the objective to use this diagram as an application tool in real projects. Regarding the electric power networks, this work applies the analysis tools provided by the theories of Complex Networks to study its topology and spatial features in order to suggest more optimal designs.Dins del paradigma de la sostenibilitat, aquesta tesi pretén aportar punts de vista complementaris als de l’enginyeria convencional amb l’objectiu de proposar eines que facilitin per una banda, trobar solucions per millorar el disseny de les línies elèctriques d’alta tensió, i per una altra optimitzar les xarxes constituïdes per aquestes. Pel que fa a la millora del disseny d’una línia d’alta tensió, s’han utilitzat les teories de les Lleis d’Escala i els Models Gravitacionals per aportar noves variables als càlculs de previsió de demanda elèctrica d’una regió. S’han proposat modificacions al diagrama vectorial de funcionament d’una línia elèctrica, conegut com a Diagrama Perrine-Baum, per incorporar les noves variables proposades amb l’objectiu que aquest diagrama pugui ser una eina d’aplicació en projectes reals. Pel que fa a les xarxes elèctriques s’han aplicat les eines d’anàlisi aportades per les teories de Xarxes Complexes per estudiar la seva topologia i les característiques espacials, amb l’objectiu de proposar dissenys més òptims.
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Orlewski, Piotr. "Modélisation des interactions anticorps-antigène : application à une maladie auto-immune, la myasthénie." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL157N.
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Ce mémoire est consacré à l'élucidation des propriétés structurales des analogues du décapeptide de la région immunogène majeure (MIR) du récepteur de l'acétylcholine (RACh) afin de détecter certaine corrélation entre leur structure et activité d'une part, et du complexe peptide MIR/anticorps d'autre part, par modélisation moléculaire. Nous avons effectué une étude comparative de la structure à l'état libre (en solution dans le DMSO et en milieu micellaire) du MIR et de plusieurs de ses [Ala]-analogues plus ou moins affines envers l'anticorps anti-RACh, et sur la structure de l'analogue [A76]MIR complexé par un anticorps monoclonal. Pour atteindre les informations structurales, nous avons mené les calculs de dynamique moléculaire sous plusieurs aspects, dans le vide et en présence explicite de molécules de solvant (dans les boites de DMSO et d'eau). Le repliement Beta I/III de la séquence NPAD est indispensable à la reconnaissance du peptide par l'anticorps anti-RACh. La partie C-terminale adopte une structure peu courante formée par un pseudocycle à 11 atomes. On observe une réorientation des chaines latérales hydrophobes qui interviennent probablement dans la reconnaissance antigène-anticorps. Nous avons appliqué la technique de modélisation par homologie de séquence à la construction de la structure 3D du fragment scFv d'un anticorps anti-RACh pour modéliser son site de liaison. Ensuite, à partir de la conformation du ligand au contact de l'anticorps, nous avons reconstitué la structure du complexe antigène-anticorps par docking
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Jebelli, Ali. "Development of Sensors and Microcontrollers for Underwater Robots." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31283.
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Nowadays, small autonomous underwater robots are strongly preferred for remote exploration of unknown and unstructured environments. Such robots allow the exploration and monitoring of underwater environments where a long term underwater presence is required to cover a large area. Furthermore, reducing the robot size, embedding electrical board inside and reducing cost are some of the challenges designers of autonomous underwater robots are facing. As a key device for reliable operation-decision process of autonomous underwater robots, a relatively fast and cost effective controller based on Fuzzy logic and proportional-integral-derivative method is proposed in this thesis. It efficiently models nonlinear system behaviors largely present in robot operation and for which mathematical models are difficult to obtain. To evaluate its response, the fault finding test approach was applied and the response of each task of the robot depicted under different operating conditions. The robot performance while combining all control programs and including sensors was also investigated while the number of program codes and inputs were increased.
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White, Angela Caroline. "Quantum field theory in curved space-time and analogue gravity in Bose-Einstein condensates." Phd thesis, 2008. http://hdl.handle.net/1885/150427.
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Slatyer, Tracy. "Analogue Hawking radiation, superradiance and sonic horizons in Bose-Einstein condensates." Thesis, 2005. http://hdl.handle.net/1885/43154.
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The propagation of fluctuations in the velocity potential of an inviscid, irrotational fluid is governed by a wave equation very similar to that governing the propagation of massless scalar fields in curved spacetime. This similarity allows certain fluid systems to be used as experimentally realisable models for objects that cannot be studied under controlled conditions, such as black holes and ultrarelativitsic rotating stars. The analogy applies only to the propagation of fields in a fixed background, not to the behaviour of the background itself. However, even this limited similarity has excited a great deal of interest from researchers, since it suggests that phenomena such as superradiance and Hawking radiation may have analogues in superfluids. In recent years, experimental advances in the creation and manipulation of Bose-Einstein condensates have provided researchers with very low temperature systems possessing a uniquely simple microscopic theory. Furthermore, under certain long-length-scale approximations, Bose-Einstein condensates can be described as classical irrotational inviscid fluids, and therefore can be treated as analogues of appropriate gravitational systems. We present a comprehensive and detailed critical review of the mean-field theory of Bose-Einstein condensates, the conditions under which Bose-Einstein condensates can be treated as an analogue gravity system, the construction of analogue black holes, and several derivations of Hawking radiation and analogue Hawking radiation. The interdisciplinary nature of analogue gravity means that the relevant results are widely scattered in the literature, and we consider this critical review and discussion of the relevant literature to be a central and noteworthy element of the project. We then analyse in detail a recent derivation of analogue Hawking radiation in Bose-Einstein condensates as a consequence of quantum depletion. We elucidate the methodology and the physical meaning of the results by comparison with the derivations of Hawking radiation considered previously, and discuss possible extensions and improvements. We also present an original investigation of analogue superradiance in simple vortices, with the vortex density profile chosen to mimic a realistic vortex in a Bose-Einstein condensate. We find that superradiant amplification occurs and is likely to be significant, but our long-length-scale approximation is of dubious validity near the scattering point.
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Wuester, Sebastian. "Classical and Quantum Field Theory of Bose-Einstein Condensates." Phd thesis, 2007. http://hdl.handle.net/1885/49265.
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Babb, James Patrick. "The derivation and quasinormal mode spectrum of acoustic anti-de sitter black hole analogues." Thesis, 2013. http://hdl.handle.net/1828/4484.
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Dumb holes (also known as acoustic black holes) are fluid flows which include an "acoustic horizon:" a surface, analogous to a gravitational horizon, beyond which sound may pass but never classically return. Soundwaves in these flows will therefore experience "effective geometries" which are identical to black hole spacetimes up to a conformal factor. By adjusting the parameters of the fluid flow, it is possible to create an effective geometry which is conformal to the Anti-de Sitter black hole spacetime- a geometry which has recieved a great deal of attention in recent years due to its conjectured holographic duality to Conformal Field Theories. While we would not expect an acoustic analogue of the AdS-CFT correspondence to exist, this dumb hole provides a means, at least in principle, of experimentally testing the theoretical properties of the AdS spacetime. In particular, I have calculated the quasinormal mode spectrum of this acoustic geometry.Graduate
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jpbabb@yahoo.ca
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Costa, Luís Filipe de Pinho Oliveira e. "General Relativity in the Framework of exact gravito-electromagnetic analogies." Doctoral thesis, 2012. https://repositorio-aberto.up.pt/handle/10216/64897.
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